The secretory process is studied in endocrine cells of the rodent neurosecretory system, anterior pituitary gland, and pancreas. Techniques employed include light and electron microscopy, enzyme cytochemistry and immunocytochemistry. Predominant areas of interest are: (1) the role of the Golgi apparatus and GERL in secretory granule formation; (2) the structural and functional association of GERL to the Golgi apparatus; (3) the role of the lysosomal system in the intracellular degradation of secretory material and internalized cell surface membrane.